Method of fabricating a synthetic quartz crystal



July 5, 1960 FREQUENCY CHANGE AF/F IN PPM J. M. STANLEY EFAL METHOD OFFABRICATING A SYNTHETIC QUARTZ CRYSTAL Filed May 7, 1956 TEMPERATURE INDEGREES CENTIGRADE INVENTOR. SERGIUS THEOKRITOFF BY JOSEPH M" STANLEY ATTORIVEY NIETHOD OF FABRICATING A SYNTHETIC QUARTZ CRYSTAL Joseph M.Stanley, Spring Lake, Sergius Theokritolf, Red Bank, Eduard A. Gerber,West Long Branch, and Andrew R. Chi, Eatontown, N.'.l., and Donald L.Hammond, Estes, Colo., assignors to the United States of America asrepresented by the Secretary of the Army 7 Filed May 7, 1956, Ser. No.583,343 p q 7 Claims ci. zszszs V (Granted under Title 35, US. Code(1952), see. 266) The invention described herein may be manufactured andused by or for the Government for governmental purposes without thepayment of any royalty thereon.

The present invention relates to synthetic quartz crystals and a methodof making the same.

Quartz crystals in natural form have long been used as piezo-electricresonators. It has been found that quartz crystals in their natural formdisplay certain inherent electrical properties. However, in manyinstances it has been found that quartz crystals having electricalproperties varying from that of natural quartz might be more desirableand appropriate in certain particular usages.

It is therefore a primary object of this invention to provide asynthetic quartz crystal having electrical properties differing fromthose of natural quartz crystals.

It is another object of the invention to provide a synthetic crystalhaving the same desirable high Q and stability of natural quartz.

Another object of the invention is to provide a means for increasing thegrowth rate of fabricated crystals incorporating the desirableproperties indicated above without imparting any undesirablecharacteristics thereto.

The above objectives and other advantages have been obtained byintroducing certain impurities during the fabrication of syntheticcrystals, such impurities being selected generally from the group ofmetals including aluminum, germanium, lead, tin and silver used eithersingly or in combination to secure certain preferred and desiredcharacteristics.

The invention can best be understood from the following description andfurther explained in the accompanying sheet of drawing in which thesingle figure of the drawing shows the frequency-temperaturecharacteristics of three different categories of crystals to beexplained in greater detail hereinafter.

In the preparation of crystals where it is desired to incorporate suchimpurities, generally the same conditions were used in all the growthsdiifering substantially only in the type of impurity element used. Whilethe size of the autoclave to be used is determined by the size of theultimate crystal desired to be obtained it has been found that excellentexperimental test sized crystals can be obtained by using autoclaveswhich ranged in size from 250-500 cc. operated in pressure ranges from5000- 6000 p.s.i.

The mean temperatures at which such operations were carried out averagedapproximately 35 0 C. as measured at the top and bottom of theautoclave; however, the specific temperatures for individual runs areindicated in the table below.

The individual runs were carried out under conditions generally used forthe growth of synthetic quartz wherein sodium carbonate solution wasutilized. The concentration of the solution was 0.5 N and the degree offill in substantially all of the cases was approximately 70 percent ofthe capacity of the autoclave and the length of runs ran from eight tofifteen days. In the table below 2,944,027} Patented July 5, 1960 ICE 2are set forth individual runs setting forth specific additiveimpurities; the concentration of the impurity in solution; theconcentration of impurity in the finished crystal as indicated in partsper million; the ionic radius; the temperature at top and bottom of theautoclave in which the run was completed, and the form of seed.

1 Temp. Cone. of Ionic at Top Run Cone. of Im- Impurity Radius and SeedNo. purity in sol. in Crystal (A) Bottom (p.p.m.) of Autoclave, 0.

A---" 0.2 N Ge+4- (is-3,000 53 339-381 Doubly oriented. B.--" 0 2 N Ge+4Ge-l,000 53 334-385 0. O 0 5 N Ge+4 Ge3,000 53 325-358 AT seed. D"---0.2 Ge 4"--- Ge1,000 53 287-344 Do. E---" 0.015 N Al+3 Al100 51 330-370Doubly oriented.

F"--- 0.015 N Al+3 Al200 51 351-399 AT seed. G---.- 0.03 N Al+3- Al-50.51 320-376 Do. H 0.015 N Al+3 Al-100--. 51 332-348 Z Seed. I 0.06 NPb+4... Pbl,000 84 315-395 AT seed. 3' 0.05 N Pb+4 b-200- 84 345-378 0K--- 0.018 N Sn+4- Sn-300- 71 311-341 Do. L 0.05 N Ag+1- Ag-200--- 1. 26350-365 Do.

The additive impurity element was introduced into the quartz growingsolution in a reactive form, for instance as a ready soluble compoundsuch as its alkali salt, e.g., sodium aluminate for aluminum or in theform of its oxide, e.g., germanium dioxide. Similarly where desired theadditive element can be added as a carbonate or other compound which canbe used conveniently.

By referring to the graph shown on the drawing there can be seen theappreciable changes of the doped units as represented by the solid linewhich represents aluminum doped synthetic quartz resonators wherein theinflection temperature, that is, the temperature for which the secondderivative of the temperature coeflicient of fiequency becomes zero, isindicated as approximately 75 C., whereas the inflection temperature ofnatural quartz resonators having approximately the same orientationangles as the doped crystals and represented by the broken lines, andthe natural quartz resonators having the same fi'equency temperaturecharacteristics as those with the doped units, as represented by thedot-dash lines have an inflection temperature of 20 C.

While there have been herein described certain preferred examples of thedoped crystals, it is obvious that modification may be made withoutdeparting from the spirit and scope of the invention as set forth in theappended claims.

What is claimed is:

1. In the fabrication of a synthetic quartz crystal, the improvementcomprising introducing aluminum into the solution from which said quartzcrystal is made in an autoclave operated in pressure ranges from5000-6000 p.s.i. at a temperature of about 350 C. for a period of from 8to '15 days.

2. In the fabrication of a synthetic quartz crystal, the improvementcomprising introducing aluminum into the solution from which said quartzcrystal is made in an autoclave operated in pressure ranges from 5000 to6000 p.s.i., at a temperature of about 350 degrees centigrade for aperiod of from 8 to 15 days and in an amount suflicient to producealuminum in solid solution within a range of 50 to 200 parts permillion.

3. In the fabrication of a synthetic quartz crystal, the improvementcomprising introducing aluminum into the solution from which said quartzcrystal is made in an autoclave operated in pressure ranges from 5000 to6000 p.s.i., at a temperature of about 350 degrees centigrade for aperiod of from 8 to 15 days and in an amount sufiicient to producealuminum in solid solution equal to suflicient to produce aluminum insolid solution equal to 50 parts per million. 200 parts per million.

4.. In t fabrication o nt eticu lertzsrysta n 1 irnprovement comprisingintroducingialuminunrinto the References IEfl 11 1.11 fileflf thlsPatent 1t ol tio from which s ua t st l-i made in an 5 UNITED STATESPATENTS 77 g autoclave operated-inpressure ranges from SQQQtofiOOO V {aof for a periodnofhfrom site a v a H .u l V. if??? $5.1: Lad -Jsllaigiggiritts tloel iroduienaluminum in solid solution equal toFOREIGNNPATENTS V I a 10 a r r 5. In the fabrication of a syntheticquartz crystal, the 1 Canada P- "1 '2" 1950 improvement comprisingintroducing aluminuminto the solution from which saidquartz crystal ismade in an 7 ,OTHER autoclave operated in pressure ranges from 5000 to6000 Hammond and Gerber: Eifeots of Impurities on Resop.s.i., at atemperature of about 350 degrees centigrade 15 nawr Propertles Quartz}!4311137, ---for a period of from 8 to"15 days and in anl amount ept m e195

1. IN THE FABRICATION OF A SYNTHETIC QUARTZ CRYSTAL, THE IMPROVEMENTCOMPRISING INTRODUCING ALUMINUM INTO THE SOLUTION FROM WHICH SAID QUARTZCRYSTAL IS MADE IN AN AUTOCLAVE OPERATED IN PRESSURE RANGE FROM5000-6000 P.S.I. AT A TEMPERATURE OF ABOUT 350*C. FOR A PERIOD OF FROM 8TO 15 DAYS.